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September 7, 2020
The surging of the induced draft fan of the boiler is like human asthma. The fan presents periodic air discharge and reverse flow, which is an unstable operating condition of abnormal performance of the centrifugal fan.
When the boiler induced draft fan surges, the airflow cycle of the entire fan pipe network system will oscillate, and there will be a kind of wheezing "whoop, whirr" noise, and even popping noise. And greatly aggravate the vibration of the fan, the bearing base will vibrate strongly, and the outlet pipe will also vibrate strongly.
Due to the strong vibration, the liquid lubrication conditions of the bearing will be destroyed, the bearing bush will burn out, and even the shaft will be twisted off, the rotor and the stator will friction and collide, and the sealing element will be severely damaged. Therefore, in actual production, the fan should be prevented from running at the surge point, and corresponding measures should be taken to solve it immediately once it runs at the surge point.
Cause of surge:
1. When the two fans are running in parallel, if the deviation of the guide vane opening is too large, the fan with a small opening will fall into the surge zone and run.
2. The flue gas duct is blocked by dust accumulation or the flue gas duct baffle is not open enough to cause excessive resistance of the system.
3. Centrifugal fan runs at low load for a long time.
Methods to deal with the surge of boiler induced draft fan:
1. When selecting the type of centrifugal fan, it should prevent the operating range from being in the surge area, and its performance should be in the high-efficiency area. Do not increase the selection factor artificially, so that the actual flow of the fan in actual operation is much higher than the design flow. If a large amount of throttling is used, it is easy to adjust the fan to the surge zone.
2. Once the centrifugal fan surging occurs during system operation, the operating condition range can be adjusted by changing the fan speed. The impeller diameter of the centrifugal fan can be changed, or it can be controlled by frequency conversion, and the air release valve can be added to change the flow rate and static pressure to avoid the surge zone.
These methods can all make the performance curve of the fan move to the small flow area, and accordingly the surge critical line will move to the small flow area, which can also expand the stable operating range of the centrifugal fan.